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A069832 Prefixing, suffixing or inserting a 7 in the number anywhere gives a prime. 9
1, 3, 9, 19, 27, 33, 39, 57, 87, 97, 159, 177, 187, 433, 487, 541, 603, 691, 717, 753, 757, 853, 949, 1257, 1471, 1707, 2277, 2367, 2617, 2953, 4317, 4507, 4623, 4779, 4797, 5773, 6481, 6757, 6777, 7017, 7351, 7417, 7471, 7479, 7747, 7797, 7813, 7977 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..2399 (terms < 10^13, first 201 terms from Harvey P. Dale)

MATHEMATICA

psi7Q[n_]:=Module[{idn=IntegerDigits[n]}, And@@PrimeQ[FromDigits/@ Table[ Insert[ idn, 7, i], {i, Length[idn]+1}]]]; Select[Range[8000], psi7Q] (* Harvey P. Dale, Sep 18 2012 *)

CROSSREFS

Cf. A068674, A068679, A069833.

Sequence in context: A056682 A032670 A068677 * A057257 A029464 A029479

Adjacent sequences:  A069829 A069830 A069831 * A069833 A069834 A069835

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Apr 14 2002

EXTENSIONS

More terms from Vladeta Jovovic, Apr 16 2002

Offset changed to 1 by Giovanni Resta, Oct 14 2019

STATUS

approved

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Last modified December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)